Automatic recloser devices are used in electrical distribution systems to protect high voltage power lines. Such devices are usually mounted to the poles or towers which suspend power lines above the ground. However, use with below ground systems is also known. The recloser device is used to minimize power distribution interruptions caused by transients or faults.
Typically, during a system disturbance, large increases in current, i.e., faults, will occur. Sensing a current increase, the recloser will open thereby cutting off current flow in order to protect distribution system components and other equipment connected to the distribution system. Since many fault conditions are temporary, the recloser is designed to close after a short period of time, thereby establishing normal current flow. For example, during a thunderstorm, if lightning were to strike the distribution system, the power to one's home may be disrupted for a few seconds causing lights and appliances to turn OFF (recloser opening), then ON (recloser closing). Once the recloser closes, if it senses the continued presence of increased current, it will again open. Such cycling between open and closed may occur three times before the recloser remains open.
A vacuum interrupter or vacuum switch is employed in many high voltage applications to perform the actual interrupting, i.e., opening and closing, function. Vacuum interrupters are used in reclosers, circuit breakers, intelligent switches for automated power distribution, and indoor switchgear. A typical vacuum interrupter comprises a pair of large-surface electrical contacts arranged in an axial configuration and enclosed within an evacuated metal-ceramic housing. One of the contacts is stationary, while the other moves in an axial direction to open and close the contacts.
In many reclosers, a number of vacuum interrupters are housed in either a single insulated enclosure or separate insulating enclosures along with related circuit components. For example, in three phase power distribution systems, separate interrupters are provided for each phase. An example of an automatic recloser for three phase use is disclosed in European Patent Application No. 580,285 A2 filed Jun. 14, 1993, entitled Auto-reclosers.
Enclosures can be filled with an insulating oil or gas (e.g. SF.sub.6) having a high dielectric strength to provide electrical insulation between the vacuum interrupters and other components. Immersing the interrupters and associated sensing devices in an insulating oil or gas allows the individual assemblies to be mounted in closer proximity, thus reducing the overall size and cost of the equipment.
The electrical utility industry has been exploring the use of polymer concrete and similar dielectric materials as a replacement for porcelain in a wide variety of insulating applications. Polymer concretes are composite materials consisting of inorganic aggregates, such as silica, bonded together with a low viscosity organic resin. The most widely known polymer concrete formulations have been trademarked by the Electric Power Research Institute under the trade name Polysil. Polymer concretes are mechanically strong and have excellent electrical properties, including a Dielectric Strength in the range of 400 V/mil. Additionally, polymer concretes can be easily molded or cast into complex shapes. Epoxy-concrete is a similar solid dielectric material wherein epoxy is used to bond the silica aggregates. Various epoxy resins which do not contain silica aggregates, such as cycloaliphatic epoxy resin, also provide similar properties.
Nonken, U.S. Pat. No. 3,812,314, discloses an interrupter assembly for use in underground electric power distribution systems that comprises a vacuum interrupter switch embedded in a bushing formed of electrically insulated epoxy resin. Reighter, U.S. Pat. No. 4,267,402, discloses an insulator formed of polymer concrete that has mounting threads molded directly into the polymer concrete. St-Jean et al., U.S. Pat. No. 4,827,370 discloses a cylindrical enclosure formed of epoxy-concrete or polymeric concrete for housing a surge arrester. Lindsey, U.S. Pat. No. 4,823,022, discloses a power line insulator formed of Polysil. PCT Application No. PCT/US94/04835, filed Apr. 28, 1994 and entitled Integrated Electrical System discloses a vacuum interrupter positioned within a molded insulator.
The problem heretofore with automatic reclosers, including reclosers having molded components, is the cumbersome and complex nature of such devices.
Another component of the automatic recloser which has received attention in the electrical utility industry is the actuator utilized to operate the vacuum interrupter. U.S. Pat. No. 4,072,918--Reed, Jr., entitled Bistable Electromagnetic Actuator and UK Patent Application No. 9409139.4 filed May 9, 1994 entitled Electromagnetic Actuators, published Nov. 15, 1995 as publication no. 2,289,374 A, each disclose electromagnetic actuators for use in recloser applications. In such actuators a coil or pair of coils, in conjunction with a permanent magnet, operate to move an armature between first and second positions.
The problem with such devices generally revolves around the number of parts included in such devices. A large number of parts has the tendency to increase the complexity of assembly. Moreover, in order to establish the necessary magnetic forces for armature movement, the electric coils require a significant level of current.
Consequently, a need still exists for an automatic recloser which avoids the use of liquids and other such insulating materials and which is less cumbersome to assemble and maintain than existing reclosers. A need also exists for such reclosers to incorporate a bi-stable electromagnetic actuator which is easy to assemble and has minimized current requirements.